The fields of ultrasonics and stress wave propagation encompass applications ranging from non-destructive testing in materials science, to beer packaging in high-volume manufacturing. Diagnostic ultrasound uses low-intensity energy, typically in the 0.1-to-20-MHz region, to determine pathological conditions or states by imaging. Therapeutic ultrasound produces a desired bio-effect, and can be divided further into two regimes, one, typically in the region of 20 kHz to 200 kHz, sometimes called low-frequency ultrasound, and the other, typically in the region from 0.2 to 10 MHz, where the wavelengths are relatively small so focused ultrasound can be used for therapy. At high intensities of energy, this application is referred to as HIFU for High Intensity Focused Ultrasound.
Examples of known therapeutic ultrasound applications are: HIFU for tumor ablation and lithotripsy, low-frequency/high amplitude phacoemulsification, thrombolysis, liposuction, neural surgery, and the use of ultrasonic scalpels for cutting and coagulation. In low-frequency ultrasound, direct contact of an ultrasonically active end-effector or surgical instrument delivers ultrasonic energy to tissue, creating bio-effects. Specifically, the instrument produces heat to coagulate and cut tissue, and cavitation to help dissect tissue planes. Other bio-effects include: ablation, accelerated bone healing and increased skin permeability for transdermal drug delivery.
At the tip of the end-effector, the energy is delivered to tissue to create several effects within the tissue. These include the basic gross conversion of mechanical energy to both frictional heat at the blade-tissue interface, and bulk heating due to viscoelastic losses within the tissue. In addition, there may be the ultrasonically induced mechanical mechanisms of: cavitation, microstreaming, micro-jet formation and sonoluminescence.
Ultrasonic medical devices are used for the safe and effective treatment of many medical conditions. Ultrasonic surgical instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end-effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end-effector, may be used to cut, dissect, or cauterize tissue. Such instruments are particularly suited for use in minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end-effector is passed through a trocar to reach the surgical site.